Drive mechanisms are used in a wide variety of applications for coupling the rotary drive of a small rapidly turning motor with a rotary driven member, such as a turret tuning mechanism or indicator for television tuners, signal seek radio tuners, and the like. Such systems require substantial speed reduction between the speed of rotation of the motor shaft and the driven member. Various approaches have been used in the past to accomplish this speed reduction, usually by worm gear speed reducing drive units or multiple gear train units. Mechanisms of both of these types are subject to considerable wear over the life of the units. Frequently, the wear results in failure of the units to operate properly, requiring their replacement or servicing, neither of which is desirable. In the case of worm gear drive mechanisms, a substantial amount of force or torque is necessary to drive them. In addition, when gear reduction units or worm gear drive units are assembled, it is necessary to effect the assembly of the entire unit between the drive motor shaft and the driven member with a fair degree of precision.
Efforts have been made in the past to overcome the disadvantages of gear train and worm gear speed reduction drive systems, and one such solution which has been proposed is disclosed in U.S. Pat. No. 3,232,128 issued Feb. 1, 1966 to Randolph, et al. This patent discloses an apparatus in which a drum to be driven encircles a pair of idler wheels each held in continuous friction contact with a reversible motor driveshaft. A clutch mechanism is utilized to move the idler wheels in a plane normal to their axis into and out of frictional contact with the inner periphery of the drum to be driven. The rotation of the idler wheels from the drive shaft then causes the drum to rotate. The direction of rotation depends upon the direction of rotation of the driveshaft. In one direction, one of the idler wheels is moved into tighter engagement with the drum to act as the driving idler while the other idler wheel moves out of engagement with the drum, and vice-versa for a reversal of the rotation direction of the driveshaft. The mechanism of this patent requires an additional clutch or spring bias to force the idler wheels into engagement with the drum, and the resultant apparatus is relatively complex.
Accordingly, it is desirable to provide an inexpensive, effecient and simple self-reversing speed reducing drive mechanism which overcomes the disadvantages of prior systems, including the system disclosed in the Randolph, et al patent.